WASHINGTON — Gov. Terry McAuliffe of Virginia used his executive power on Friday to restore voting rights to more than 200,000 convicted felons, circumventing the Republican-run legislature. The action effectively overturns a Civil War-era provision in the state’s Constitution aimed, he said, at disenfranchising African-Americans.

The sweeping order, in a swing state that could play a role in deciding the November presidential election, will enable all felons who have served their prison time and finished parole or probation to register to vote. Nearly half are African-American, a core constituency of Democrats, Mr. McAuliffe’s political party.

Amid intensifying national attention over harsh sentencing policies that have disproportionately affected African-Americans, governors and legislatures around the nation have been debating — and often fighting over — moves to restore voting rights for convicted felons. Virginia imposes especially harsh restrictions, barring felons from voting for life.

In Kentucky, Gov. Matt Bevin, a newly elected Republican, recently overturned an order enacted by his Democratic predecessor that was similar to the one Mr. McAuliffe signed Friday. In Maryland, Gov. Larry Hogan, a Republican, vetoed a measure to restore voting rights to convicted felons, but Democrats in the state legislature overrode him in February and an estimated 44,000 former prisoners who are on probation can now register to vote.

“There’s no question that we’ve had a horrible history in voting rights as relates to African-Americans — we should remedy it,” Mr. McAuliffe said in an interview Thursday, previewing the announcement he made on the steps of Virginia’s Capitol, just yards from where President Abraham Lincoln once addressed freed slaves. “We should do it as soon as we possibly can.”

Republicans in the Virginia Legislature have resisted measures to expand voting rights for convicted felons, and Mr. McAuliffe’s action, which he said was justified under an expansive legal interpretation of his executive clemency authority, provoked an immediate backlash. Virginia Republicans issued a statement Friday accusing the governor of “political opportunism” and “a transparent effort to win votes.”

“Those who have paid their debts to society should be allowed full participation in society,” said the statement from the party chairman, John Whitbeck. “But there are limits.” He said Mr. McAuliffe was wrong to issue a blanket restoration of rights, even to those who “committed heinous acts of violence.”

The order includes those convicted of violent crimes, including murder and rape. There is no way to know how many of the newly eligible voters in Virginia will register. “My message is going to be that I have now done my part,” Mr. McAuliffe said.

Nationally, an estimated 5.85 million Americans are denied the right to vote because of felony convictions, according to The Sentencing Project, a Washington research organizations, which says one in five African-Americans in Virginia cannot vote.

Only two states, Maine and Vermont, have no voting restrictions on felons; Virginia is among four – the others are Kentucky, Florida and Iowa – that have the harshest restrictions.

Friday’s shift in Virginia is part of a national trend toward restoring voter rights to felons, based in part on the hope that it will aid former prisoners’ re-entry into society. Over the last two decades about 20 states have acted to ease their restrictions, according to the Brennan Center for Justice at New York University.

In Kentucky, Mr. Bevin, who took office in November, promptly overturned an executive order issued by his predecessor, Steven L. Beshear, just before he left office. Then, last week, Mr. Bevin signed into law a less expansive measure, allowing felons to petition judges to vacate their convictions, which would enable them to vote.

Previous governors in Florida and Iowa took executive action to ease their lifetime bans, but in each case, a subsequent governor restored the tough rules.

Marc Mauer, executive director of the Sentencing Project, said Mr. McAuliffe’s decision would have lasting consequences because it will remain in effect at least until January 2018, when the governor leaves office.

“This will be the single most significant action on disenfranchisement that we’ve ever seen from a governor,” Mr. Mauer said, “and it’s noteworthy that it’s coming in the middle of this term, not the day before he leaves office. So there may be some political heat but clearly he’s willing to take that on, which is quite admirable.”

Myrna Pérez, director of a voting rights project at the Brennan Center, said Mr. McAuliffe’s move was particularly important because Virginia has had such restrictive laws on voting by felons. Still, she said,“Compared to the rest of the country, this is a very middle of the road policy.’’

Ms. Pérez said a number of states already had less restrictive policies than the one announced by Mr. McAuliffe. Fourteen states allow felons to vote after their prison terms are completed even while they remain on parole or probation.

Advocates who have been working with the Virginia governor say they are planning to fan out into Richmond communities Friday to start registering people.

Experts say with the stroke of his pen, Mr. McAuliffe has allowed convicted felons to begin registering to vote, and that their voting rights cannot be revoked — even if a new governor rescinds the order for future released prisoners.

But the move led to accusations that the governor was playing politics; he is a longtime friend of — and fund-raiser for — Hillary Clinton, the likely Democratic nominee for president, and former President Bill Clinton.

In the interview, Mr. McAuliffe said that he was not acting for political reasons, and that few people outside his immediate staff knew of his plan. He said he did not consult with Mrs. Clinton or her campaign before making the decision.

The executive order builds on steps the governor had already taken to restore voting rights to 18,000 Virginians since the beginning of his term, and he said he believed his authority to issue the decision was “ironclad.”

Prof. A. E. Dick Howard of the University of Virginia School of Law, the principal draftsman of a revised Constitution adopted by Virginia in 1971, agreed, and said the governor had “ample authority.” But Professor Howard, who advised Mr. McAuliffe on the issue, said the move might well be challenged in court. The most likely argument, he said, is that the governor cannot restore voting rights to an entire class of people all at once.

Virginia’s Constitution has prohibited felons from voting since the Civil War; the restrictions were expanded in 1902, as part of a package that included poll taxes and literacy tests.

In researching the provisions, advisers to the governor turned up a 1906 report that quoted Carter Glass, a Virginia state senator, as saying they would “eliminate the darkey as a political factor in this State in less than five years, so that in no single county of the Commonwealth will there be the least concern felt for the complete supremacy of the white race in the affairs of government.”

Mr. McAuliffe, who took office in 2014 and campaigned to restore voting rights to felons, said that he viewed disenfranchisement as “a remnant of the poll tax” and that he had been “trying to figure out what more I can possibly do.”

The governor’s action Friday will not apply to felons released in the future; his aides say Mr. McAuliffe intends to issue similar orders on a monthly basis to cover people as they are released.

“People have served their time and done their probation,” Mr. McAuliffe said. “I want you back in society. I want you feeling good about yourself. I want you voting, getting a job, paying taxes.’’

Correction:

An article on April 23 about an executive order issued by Gov. Terry McAuliffe of Virginia that expanded voting rights for convicted felons, using information from the governor’s office, overstated the law’s effect on African-Americans. A subsequent analysis by the governor’s office showed that 45 percent — not a majority — of those affected were African-American. This correction was delayed because the error was not brought to the attention of editors until Thursday.

Sheryl Gay Stolberg reported from Washington and Erik Eckholm from New York